The present invention relates to a miniature electronic timepiece whose time-indicating hands are driven by the rotor of a stepping motor, and more particularly to an electronic system which includes means to apply drive pulses to the stator coil of the motor and to short circuit the stator coil at the conclusion of each drive pulse to brake the rotor.
In small electronic timepieces (miniature electronic timepieces), the available voltage of the d.c. feed source (miniature battery, solar cells, etc.) does not always have the value required for powering the timepiece or individual components thereof. For this reason, it has already been proposed to chop the voltage of the d.c. source to produce a periodic voltage and then to effect transformation thereof, whereupon the transformed voltage is rectified, thus making available a voltage which is higher or lower than the voltage of the feed source.
The reduction of the feed voltage can, for example, be meaningful if it is desired to feed an integrated circuit with a voltage which is lower than the voltage of a feed voltage battery, so as to keep the current consumption of the circuit at the lowest possible level and thereby prolong the service life of the battery. In actual fact, the power requirement of such a circuit is proportional to the square of the voltage. Thus, it is desirable to keep at the lowest possible level the feed voltage of the solid state circuit, in particular of the oscillator circuit operating at relatively high frequency and normally stabilized by a quartz crystal. For example, reduction of the d.c. voltage feeding the solid state circuit by 50% reduces the energy consumption by 75%.
In other cases, it is desirable to increase an available voltage (since electrochromic or other display elements require a higher voltage than the remaining components of the timepiece, or because it is desired to feed the timepiece with a thermo-element battery, a solar cell battery or the like; i.e., with a source of energy the voltage of which does not attain the value normally required for entirely satisfactory operartion of the timepiece).
The need to provide a voltage converter in such a miniature timepiece constitutes a drawback. On the one hand, such a voltage converter, since it requires a transformer, is relatively costly. Moreover, the voltage transformer requires an excessive amount of space. These disadvantages are contrary to the demands made on modern electronic timepieces (simple and inexpensive manufacturability, a design as compact as possible, accompanied by a high order of accuracy and reliability).
For some time, there have been manufactured and put on the market to an increasing extent quartz-crystal wrist watches, the hands of which are driven by a stepping motor. Also in such cases, an increase or reduction of the d-c voltage frequently appears to be desirable (for example, for feeding digital display elements in order to display the seconds and/or the display of a stopped time period). However, the stepping motor is relatively bulky, thus leaving little space for a voltage transformer. As a consequence, the space problem in such watches is troublesome.